1. Field of the Invention
This invention relates to an overlock sewing machine and more particularly, to a threading unit thereof.
2. Related Art Statement
The work of passing a thread through a needle is very difficult even for an operator with normal eyesight; therefore, various types of threading units have been proposed. For example, a first type ( as disclosed in Japanese Utility Model Application Laid-Open No. 53-35061 or No. 61-35188) uses a control member by which a thread setting member, such as a thread setting hook or a threading wire, is passed through the eye of a needle, and after a thread is hitched to the thread setting member or passed therethrough, the thread setting member is retracted. A second type ( as disclosed in Japanese Patent Aplication Laid-Open No. 50-37548 or Japanese Utility Model Application Laid-Open No. 55-37096) utilizes air flow or its suctional action.
However, the foregoing types of threading units generally are not adaptable for the overlock sewing machine equipped with a looper, a cloth cutting knife, etc. because of mechanical complexity; thus, no overlock sewing machine has been proposed to be equipped with any threading unit.
Some prior art types have thread setting mechanisms simplified in configuration, but require delicate control timing and skill.
Further, according to the conventional threading unit, the needle must be positioned at a given position, e.g. a top dead point to pass the thread setting member through the eye of the needle; hence, a needle positioner is provided separately from the threading unit.
However, the needle positioner is expensive and renders the mechanism complicated.